Greaves, H. R. G.
George Allen and Unwin, 1958
Buku Teks
Carnoy, Martin
Princeton University press, 1984
Buku Teks
McDonald, Lee Cameron, author
Harcour Brace Jovanwich, 1968
Buku Teks
Fowler, Robert Booth, author
Praeger, 1985
Buku Teks
Sabine, George H., author
George G. Harrap, 1952
Buku Teks